At present there are integrated ROM, EPROM or EEPROM circuits, which can be read or read and written by a power supply using a suitable external reading/writing device. In such cases information is transmitted in serial form by superimposing signals on the supply voltage. Transmission to the inside of the integrated circuit takes place by amplitude modulated voltage signals superimposed on the supply voltage, said signals being generated by the reading/writing device, whereas transmission to the outside of the integrated circuit takes place by current signals generated by the integrated circuit and superimposed on the base current consumed by it.
This procedure is simple, but can be relatively unreliable due to poor contacts and interference of all types which can deform the signals and falsify their interpretation.